Most modern portable devices, such as smartphones, have built in global positioning system (GPS) capabilities which facilitate a variety of location based applications. One problem with most widespread location systems including GPS, cellular identification (ID) and wireless fidelity (WiFi) based location systems, is that they cannot function in underground transportation systems because there is no access to a GPS satellite or a mobile network. However, users of underground transportation systems would greatly benefit from knowledge of their location, especially when traveling in unfamiliar cities. For example, knowledge of their precise underground location can facilitate route planning and forewarn users of train stops at which they should depart. Most conventional solutions for enabling underground location systems involve large installations of hotspots throughout the transportation system. Such solutions are costly and inefficient.